The passive containment cooling system (PCS) provides the safety-related ultimate heat sink for the plant (see Fig. 5). The
PCS cools the containment following an accident so that design pressure is not exceeded and pressure is rapidly reduced. The
steel containment vessel provides the heat transfer surface that removes heat from inside the containment and transfers it to
the atmosphere. Heat is removed from the containment vessel by the continuous, natural circulation of air. During an
accident, air cooling is supplemented by water evaporation. The water drains by gravity from a tank located on top of the
containment shield building.